468 lines
15 KiB
XML
468 lines
15 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink">
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<title>Installing NixOS</title>
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<!--===============================================================-->
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<section>
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<title>Obtaining NixOS</title>
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<para>NixOS ISO images can be downloaded from the <link
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xlink:href="http://nixos.org/nixos/download.html">NixOS
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homepage</link>. These can be burned onto a CD. It is also possible
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to copy them onto a USB stick and install NixOS from there. For
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details, see the <link
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xlink:href="https://nixos.org/wiki/Installing_NixOS_from_a_USB_stick">NixOS
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Wiki</link>.</para>
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<para>As an alternative to installing NixOS yourself, you can get a
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running NixOS system through several other means:
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<itemizedlist>
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<listitem>
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<para>Using virtual appliances in Open Virtualization Format (OVF)
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that can be imported into VirtualBox. These are available from
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the <link xlink:href="http://nixos.org/nixos/download.html">NixOS
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homepage</link>.</para>
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</listitem>
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<listitem>
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<para>Using AMIs for Amazon’s EC2. To find one for your region
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and instance type, please refer to the <link
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xlink:href="https://github.com/NixOS/nixops/blob/master/nix/ec2-amis.nix">list
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of most recent AMIs</link>.</para>
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</listitem>
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<listitem>
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<para>Using NixOps, the NixOS-based cloud deployment tool, which
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allows you to provision VirtualBox and EC2 NixOS instances from
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declarative specifications. Check out the <link
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xlink:href="https://github.com/NixOS/nixops">NixOps
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homepage</link> for details.</para>
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</listitem>
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</itemizedlist>
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</para>
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</section>
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<!--===============================================================-->
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<section>
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<title>Installation</title>
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<orderedlist>
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<listitem><para>Boot from the CD.</para></listitem>
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<listitem><para>The CD contains a basic NixOS installation. (It
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also contains Memtest86+, useful if you want to test new hardware.)
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When it’s finished booting, it should have detected most of your
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hardware and brought up networking (check
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<command>ifconfig</command>). Networking is necessary for the
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installer, since it will download lots of stuff (such as source
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tarballs or Nixpkgs channel binaries). It’s best if you have a DHCP
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server on your network. Otherwise configure networking manually
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using <command>ifconfig</command>.</para></listitem>
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<listitem><para>The NixOS manual is available on virtual console 8
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(press Alt+F8 to access).</para></listitem>
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<listitem><para>Login as <literal>root</literal> and the empty
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password.</para></listitem>
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<listitem><para>If you downloaded the graphical ISO image, you can
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run <command>start display-manager</command> to start KDE.</para></listitem>
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<listitem><para>The NixOS installer doesn’t do any partitioning or
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formatting yet, so you need to that yourself. Use the following
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commands:
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<itemizedlist>
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<listitem><para>For partitioning:
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<command>fdisk</command>.</para></listitem>
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<listitem><para>For initialising Ext4 partitions:
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<command>mkfs.ext4</command>. It is recommended that you assign a
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unique symbolic label to the file system using the option
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<option>-L <replaceable>label</replaceable></option>, since this
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makes the file system configuration independent from device
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changes. For example:
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<screen>
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$ mkfs.ext4 -L nixos /dev/sda1</screen>
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</para></listitem>
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<listitem><para>For creating swap partitions:
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<command>mkswap</command>. Again it’s recommended to assign a
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label to the swap partition: <option>-L
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<replaceable>label</replaceable></option>.</para></listitem>
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<listitem><para>For creating LVM volumes, the LVM commands, e.g.,
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<screen>
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$ pvcreate /dev/sda1 /dev/sdb1
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$ vgcreate MyVolGroup /dev/sda1 /dev/sdb1
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$ lvcreate --size 2G --name bigdisk MyVolGroup
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$ lvcreate --size 1G --name smalldisk MyVolGroup</screen>
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</para></listitem>
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<listitem><para>For creating software RAID devices, use
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<command>mdadm</command>.</para></listitem>
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</itemizedlist>
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</para></listitem>
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<listitem><para>Mount the target file system on which NixOS should
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be installed on <filename>/mnt</filename>, e.g.
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<screen>
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$ mount /dev/disk/by-label/nixos /mnt
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</screen>
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</para></listitem>
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<listitem><para>If your machine has a limited amount of memory, you
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may want to activate swap devices now (<command>swapon
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<replaceable>device</replaceable></command>). The installer (or
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rather, the build actions that it may spawn) may need quite a bit of
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RAM, depending on your configuration.</para></listitem>
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<listitem>
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<para>You now need to create a file
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<filename>/mnt/etc/nixos/configuration.nix</filename> that
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specifies the intended configuration of the system. This is
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because NixOS has a <emphasis>declarative</emphasis> configuration
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model: you create or edit a description of the desired
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configuration of your system, and then NixOS takes care of making
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it happen. The syntax of the NixOS configuration file is
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described in <xref linkend="sec-configuration-syntax"/>, while a
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list of available configuration options appears in <xref
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linkend="ch-options"/>. A minimal example is shown in <xref
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linkend="ex-config"/>.</para>
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<para>The command <command>nixos-generate-config</command> can
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generate an initial configuration file for you:
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<screen>
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$ nixos-generate-config --root /mnt</screen>
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You should then edit
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<filename>/mnt/etc/nixos/configuration.nix</filename> to suit your
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needs:
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<screen>
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$ nano /mnt/etc/nixos/configuration.nix
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</screen>
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The <command>vim</command> text editor is also available.</para>
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<para>You <emphasis>must</emphasis> set the option
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<option>boot.loader.grub.device</option> to specify on which disk
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the GRUB boot loader is to be installed. Without it, NixOS cannot
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boot.</para>
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<para>Another critical option is <option>fileSystems</option>,
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specifying the file systems that need to be mounted by NixOS.
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However, you typically don’t need to set it yourself, because
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<command>nixos-generate-config</command> sets it automatically in
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<filename>/mnt/etc/nixos/hardware-configuration.nix</filename>
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from your currently mounted file systems. (The configuration file
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<filename>hardware-configuration.nix</filename> is included from
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<filename>configuration.nix</filename> and will be overwritten by
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future invocations of <command>nixos-generate-config</command>;
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thus, you generally should not modify it.)</para>
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<note><para>Depending on your hardware configuration or type of
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file system, you may need to set the option
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<option>boot.initrd.kernelModules</option> to include the kernel
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modules that are necessary for mounting the root file system,
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otherwise the installed system will not be able to boot. (If this
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happens, boot from the CD again, mount the target file system on
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<filename>/mnt</filename>, fix
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<filename>/mnt/etc/nixos/configuration.nix</filename> and rerun
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<filename>nixos-install</filename>.) In most cases,
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<command>nixos-generate-config</command> will figure out the
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required modules.</para></note>
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<para>Examples of real-world NixOS configuration files can be
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found at <link
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xlink:href="https://nixos.org/repos/nix/configurations/trunk/"/>.</para>
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</listitem>
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<listitem><para>Do the installation:
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<screen>
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$ nixos-install</screen>
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Cross fingers. If this fails due to a temporary problem (such as
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a network issue while downloading binaries from the NixOS binary
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cache), you can just re-run <command>nixos-install</command>.
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Otherwise, fix your <filename>configuration.nix</filename> and
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then re-run <command>nixos-install</command>.</para></listitem>
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<listitem><para>If everything went well:
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<screen>
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$ reboot</screen>
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</para></listitem>
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<listitem>
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<para>You should now be able to boot into the installed NixOS.
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The GRUB boot menu shows a list of <emphasis>available
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configurations</emphasis> (initially just one). Every time you
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change the NixOS configuration (see <xref
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linkend="sec-changing-config" />), a new item appears in the menu.
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This allows you to easily roll back to another configuration if
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something goes wrong.</para>
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<para>You should log in and change the <literal>root</literal>
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password with <command>passwd</command>.</para>
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<para>You’ll probably want to create some user accounts as well,
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which can be done with <command>useradd</command>:
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<screen>
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$ useradd -c 'Eelco Dolstra' -m eelco
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$ passwd eelco</screen>
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</para>
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<para>You may also want to install some software. For instance,
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<screen>
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$ nix-env -qa \*</screen>
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shows what packages are available, and
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<screen>
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$ nix-env -i w3m</screen>
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install the <literal>w3m</literal> browser.</para>
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</listitem>
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</orderedlist>
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<para>To summarise, <xref linkend="ex-install-sequence" /> shows a
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typical sequence of commands for installing NixOS on an empty hard
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drive (here <filename>/dev/sda</filename>). <xref linkend="ex-config"
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/> shows a corresponding configuration Nix expression.</para>
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<example xml:id='ex-install-sequence'><title>Commands for installing NixOS on <filename>/dev/sda</filename></title>
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<screen>
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$ fdisk /dev/sda # <lineannotation>(or whatever device you want to install on)</lineannotation>
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$ mkfs.ext4 -L nixos /dev/sda1
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$ mkswap -L swap /dev/sda2
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$ swapon /dev/sda2
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$ mount /dev/disk/by-label/nixos /mnt
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$ nixos-generate-config --root /mnt
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$ nano /mnt/etc/nixos/configuration.nix
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$ nixos-install
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$ reboot</screen>
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</example>
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<example xml:id='ex-config'><title>NixOS configuration</title>
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<screen>
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{ config, pkgs, ... }:
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{
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imports =
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[ # Include the results of the hardware scan.
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./hardware-configuration.nix
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];
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boot.loader.grub.device = "/dev/sda";
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# Note: setting fileSystems is generally not
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# necessary, since nixos-generate-config figures them out
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# automatically in hardware-configuration.nix.
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#fileSystems."/".device = "/dev/disk/by-label/nixos";
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# Enable the OpenSSH server.
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services.sshd.enable = true;
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}</screen>
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</example>
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</section>
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<!--===============================================================-->
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<section xml:id="sec-changing-config">
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<title>Changing the configuration</title>
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<para>The file <filename>/etc/nixos/configuration.nix</filename>
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contains the current configuration of your machine. Whenever you’ve
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changed something to that file, you should do
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<screen>
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$ nixos-rebuild switch</screen>
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to build the new configuration, make it the default configuration for
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booting, and try to realise the configuration in the running system
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(e.g., by restarting system services).</para>
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<warning><para>These commands must be executed as root, so you should
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either run them from a root shell or by prefixing them with
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<literal>sudo -i</literal>.</para></warning>
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<para>You can also do
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<screen>
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$ nixos-rebuild test</screen>
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to build the configuration and switch the running system to it, but
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without making it the boot default. So if (say) the configuration
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locks up your machine, you can just reboot to get back to a working
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configuration.</para>
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<para>There is also
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<screen>
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$ nixos-rebuild boot</screen>
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to build the configuration and make it the boot default, but not
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switch to it now (so it will only take effect after the next
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reboot).</para>
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<para>You can make your configuration show up in a different submenu
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of the GRUB 2 boot screen by giving it a different <emphasis>profile
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name</emphasis>, e.g.
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<screen>
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$ nixos-rebuild switch -p test </screen>
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which causes the new configuration (and previous ones created using
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<literal>-p test</literal>) to show up in the GRUB submenu “NixOS -
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Profile 'test'”. This can be useful to separate test configurations
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from “stable” configurations.</para>
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<para>Finally, you can do
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<screen>
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$ nixos-rebuild build</screen>
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to build the configuration but nothing more. This is useful to see
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whether everything compiles cleanly.</para>
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<para>If you have a machine that supports hardware virtualisation, you
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can also test the new configuration in a sandbox by building and
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running a QEMU <emphasis>virtual machine</emphasis> that contains the
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desired configuration. Just do
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<screen>
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$ nixos-rebuild build-vm
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$ ./result/bin/run-*-vm
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</screen>
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The VM does not have use any data from your host system, so your
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existing user accounts and home directories will not be
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available.</para>
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</section>
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<!--===============================================================-->
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<section xml:id="sec-upgrading">
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<title>Upgrading NixOS</title>
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<para>The best way to keep your NixOS installation up to date is to
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use one of the NixOS <emphasis>channels</emphasis>. A channel is a
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Nix mechanism for distributing Nix expressions and associated
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binaries. The NixOS channels are updated automatically from NixOS’s
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Git repository after certain tests have passed and all packages have
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been built. These channels are:
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<itemizedlist>
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<listitem>
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<para>Stable channels, such as <literal
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xlink:href="http://nixos.org/channels/nixos-13.10">nixos-13.10</literal>.
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These only get conservative bug fixes and package upgrades. For
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instance, a channel update may cause the Linux kernel on your
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system to be upgraded from 3.4.66 to 3.4.67 (a minor bug fix), but
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not from 3.4.<replaceable>x</replaceable> to
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3.11.<replaceable>x</replaceable> (a major change that has the
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potential to break things).</para>
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</listitem>
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<listitem>
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<para>The unstable channel, <literal
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xlink:href="http://nixos.org/channels/nixos-unstable">nixos-unstable</literal>.
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This corresponds to NixOS’s main development branch, and may thus
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see radical changes between channel updates. It’s not recommended
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for production systems.</para>
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</listitem>
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</itemizedlist>
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To see what channels are available, go to <link
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xlink:href="http://nixos.org/channels"/>. (Note that the URIs of the
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various channels redirect to a directory that contains the channel’s
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latest version and includes ISO images and VirtualBox
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appliances.)</para>
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<para>When you first install NixOS, you’re automatically subscribed to
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the NixOS channel that corresponds to your installation source. For
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instance, if you installed from a 13.10 ISO, you will be subscribed to
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the <literal>nixos-13.10</literal> channel. To see which NixOS
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channel you’re subscribed to, run the following as root:
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<screen>
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$ nix-channel --list | grep nixos
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nixos https://nixos.org/channels/nixos-unstable
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</screen>
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To switch to a different NixOS channel, do
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<screen>
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$ nix-channel --add http://nixos.org/channels/<replaceable>channel-name</replaceable> nixos
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</screen>
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(Be sure to include the <literal>nixos</literal> parameter at the
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end.) For instance, to use the NixOS 13.10 stable channel:
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<screen>
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$ nix-channel --add http://nixos.org/channels/nixos-13.10 nixos
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</screen>
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But it you want to live on the bleeding edge:
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<screen>
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$ nix-channel --add http://nixos.org/channels/nixos-unstable nixos
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</screen>
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</para>
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<para>You can then upgrade NixOS to the latest version in your chosen
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channel by running
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<screen>
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$ nixos-rebuild switch --upgrade
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</screen>
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which is equivalent to the more verbose <literal>nix-channel --update
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nixos; nixos-rebuild switch</literal>.</para>
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<warning><para>It is generally safe to switch back and forth between
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channels. The only exception is that a newer NixOS may also have a
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newer Nix version, which may involve an upgrade of Nix’s database
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schema. This cannot be undone easily, so in that case you will not be
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able to go back to your original channel.</para></warning>
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</section>
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</chapter>
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